Air-sea CO2 exchange over the Gulf of Finland according to SOCOM ship measurements during March and April 2019 have been assessed to determine the possible impact of the water surface on estimates of St. Petersburg anthropogenic emissions. It was found that the surface of the Gulf of Finland is a source of CO2 in March and a sink in April 2019. CO2 fluxes per unit area of the water surface of the Gulf of Finland were on average significantly smaller (by 1-2 orders) than the anthropogenic emissions of St. Petersburg. Contribution of the Gulf of Finland surface to CO2 content of air masses passing over the water surface in March-April 2019 was small on average in comparison with the contribution of St. Petersburg according to EMME (Emission Monitoring Mobile Experiment) measurements and ODIAC data (less than 1% of the cities contribution). For extreme wind speeds above the water surface and differences in the partial CO2 pressure in water and air, the contribution of the Gulf of Finland to the CO2 content of the air masses can reach almost 3% in relation to the anthropogenic contribution of St. Petersburg.